… Additional patrols will follow in coming weeks, and could also be conducted around features that have been built up by Vietnam and the Philippines in the Spratlys, a U.S. defense official told the Reuters news agency.

“This is something that will be a regular occurrence, not a one-off event,” the official said, also speaking on condition of anonymity. “It’s not something that’s unique to China.”

At the U.S. Naval War College in Newport, R.I., associate professor Andrew Erickson said the U.S action underscored its “commitment to maintaining an open global system with global commons that all are free to use to the maximum extent permitted by international law.”

“As can be seen from the operation’s peaceful, unimpeded nature, China and the U.S. share an interest in keeping the vital sea lanes of the South China Sea stable and open,” he said.

China has built small islands on top of previously submerged reefs like Subi and is in the process of smoothing and reinforcing runways suitable for military aircraft. According to international law, experts said no country can claim more than a 500-meter safety zone around a previously submerged reef. …

Further thoughts from Andrew Erickson:

Beyond 500 meters of low-tide elevations (LTEs)—features naturally below water at high tide—foreign ships and aircraft are free to operate at will without consultation or permission, as USS Lassen has just done near Subi Reef. Unlike rocks or islands, under international law, LTEs such as Subi are not entitled to the 12 nautical miles’ territorial waters or airspace that rocks or islands are. Rather, beyond a 500-meter safety zone, all high seas freedoms apply. These are the freedoms that USS Lassen has just exercised.

The USS Lassen’s positive action underscores U.S. commitment to maintaining an open global system with global commons that are free for all to use to the maximum extent permitted by international law, without favor, fear, or obstruction. Freedom of the Seas is a key element of this vital equation.

As can be seen from the peaceful, unimpeded nature of the USS Lassen’s operation, China and the U.S. share an interest in keeping the South China Sea’s vital sea lanes of stable and open.